Audio BT uses a different BT protocol than the serial protocol. Also it's buffered. But the buffering only replaces many intermittent delays with one big long delay. 
AV sync is handled at the application level, not in the BT channel itself.
Audio BT uses a different BT protocol than the serial protocol. Also it's buffered. But the buffering only replaces many intermittent delays with one big long delay. AV sync is handled at the application level, not in the BT channel itself.